The Metabolism of Sympathomimetic Bronchodilator Drugs by the Isolated Perfused Dog Lung

Abstract

1. The metabolism of three bronchodilator drugs, isoprenaline, isoetharine and terbutaline, was studied in the isolated perfused dog lung.

2. Isoprenaline and isoetharine, administered into the vascular system or the bronchial tree, were extensively O-methylated and this pattern of metabolism was reflected in the drug accumulated in lung tissue.

3. Approximately 30% of isoprenaline absorbed from the airways was converted to 3-O-methylisoprenaline in its first pass through the lung.

4. Terbutaline, which is not a catecholamine, was not significantly metabolized by the lung.

5. None of these drugs or their O-methyl metabolites was conjugated in significant amounts by the lungs, nor were acidic metabolites, from attack by monoamine oxidase, observed.